a. Field of the Invention
The present invention relates generally to medical systems for performing therapeutic functions, such as, for example, ablation procedures. More particularly, the present invention relates to an ablation system that includes blood leakage minimization and/or tissue protective capabilities.
b. Background Art
It is known to use minimally invasive surgical devices or ablating tools to perform ablation procedures in, for example, the heart. For instance, in treating a condition known as atrial fibrillation, it is known to advance an ablating tool through the vasculature of a patient to a desired location, and to then thermally ablate tissue within, for example, an ostium (OS) connecting a pulmonary vein to the heart, or to ablate the tissue within the heart surrounding the OS.
One example of a type of tool known in the art to perform such procedures is a catheter-based ablating device such as that or those described in U.S. Pat. No. 6,635,054 entitled “Thermal Treatment Methods and Apparatus with Focused Energy Application,” U.S. Patent Publication No. 2004/0176757 entitled “Cardiac Ablation Devices,” and International Publication No. WO 2005/102199 entitled “Ablation Devices with Sensor Structures.” These known devices generally include, among other components, an elongate shaft having a proximal end, a distal end, and a longitudinal axis extending therebetween. The devices further include an ablation element mounted at or near the distal end of the elongate shaft. In at least one such device, the ablation element comprises a pair of inflatable balloons that share a common wall therebetween, with one of the balloons being disposed proximally of the other balloon. The balloons are configured to have a collapsed condition and an expanded condition, and are configured such that one is liquid or fluid inflated and one is gas inflated. The ablation element further includes an ultrasound transducer mounted or otherwise disposed within the distally disposed balloon that is configured to emit high intensity ultrasonic waves radially outwardly into the liquid or fluid within the balloon with respect to the longitudinal axis of the elongate shaft. The ultrasonic waves have the strength and intensity to burn or ablate tissue after they are reflectively focused forward (more distally onto the OS interior) by the reflectively curved fluid/gas interface defined, in part, by the common wall shared by the two overlying balloons.
In operation, once such an ablating device is positioned in a desired location within the patient's anatomy (e.g., in a pulmonary vein OS), the balloons are respectively inflated with saline (inner balloon) and carbon dioxide gas (outer balloon). The ultrasound transducer is then selectively activated to emit ablating energy (e.g., intense ultrasonic waves). When the ultrasound transducer, which is typically cylindrical, emits the ultrasonic waves in radial directions into the fluid-filled balloon, the waves are reflected and redirected (focused) forward by the common reflective interface wall between the two balloons, and re-directed forward of the balloons and focused to define, for example, a focused ring-like ablation region in the circumferential interior OS annular wall. Such radial or circumferential ablating devices provide an efficient and effective means by which to simultaneously circumferentially ablate myocardial tissue around the OS of the pulmonary vein. Typically, multiple pulmonary ostia are ablated separately and sequentially with the same device as it is moved and placed in each OS needing ablation.
However, these known devices are not without their drawbacks. For instance, one function of the balloons of the ablating device, when the ablation element is inserted within an orifice or OS and inflated, is to serve as a blood flow barrier to seal the interface between the balloons and the inner annular wall of the orifice or OS, thereby temporarily preventing blood flow past the balloons through the OS. If the blood flow is not stopped substantially completely around all 360 degrees, then the residual blood flow may prevent thermal lesioning due to unwanted cooling of target tissues. However, when the balloons are manufactured and then inflated, they are manufactured and inflated to be rotationally symmetric (bodies of revolution) because it is the most manufacturable approach and does not require any rotational device alignment to target tissues. Conversely, the orifices or ostia within which the device, and the ablation element thereof, in particular, is to be inserted are not typically rotationally symmetric, but rather oftentimes are irregular and have a more oval or oblong shape with, for example, as much as a 3:1 aspect ratio. As such, when the balloons are inflated in an oval-shaped or irregular orifice, a sealed (to blood flow) interface between the balloon(s) and OS cannot be created, and as a result, cooling blood may leak past the balloons across the interface where ablative heating is to take place. When the blood leaks past the balloon(s), it undesirably serves to cool the surface of the tissue over which it flows, and does so in a non-uniform manner that cannot be easily corrected or compensated for. This is undesirable as these unintended cooled areas of tissue cannot be sufficiently continuously ablated or burned because they are being cooled by the blood, therefore, surface lesions cannot be controllably formed. Accordingly, the quality and adequacy of the ablation procedure may be substantially reduced, or require additional ablating procedures to be performed in order to complete the desired continuous ablation lesion of the targeted tissue.
Another drawback in known endocardial catheter pulmonary vein ostia ablation systems relates to the monitoring, maintenance, and/or control of the temperature in non-targeted tissue proximate the targeted ablation site during the ablation procedure. Such non-targeted tissue must not be damaged during the ablation procedure. More particularly, when certain heart tissue is being ablated, the energy emitted from the ablating device may be strong enough or generate a high enough temperature to cause tissue necrosis in non-targeted tissue. For example, portions of the esophagus are located proximate the heart and if an endocardial ablation site is near the esophagus the ablation energy itself, or heat generated by it and conducted away from the target, can potentially cause the nearby esophageal tissue to experience cell death.
Conventional suggested methods of addressing this concern include the use of one or more thermocouples or thermistor-based sensors that are passed either blindly or with the assistance of imaging or visualization systems (e.g., fluoroscopic, impedance-based, MRI, etc.) down the throat on an expandable member configured to monitor the temperature of the esophageal tissue and detect undesirable energy transfer to the esophagus. Such a technique may require the use of a dense macroscopic thermistor array, which may result in a disposable temperature monitoring device being cost-prohibitive or large. Additionally, such a technique may cause challenges with respect to the accuracy of the placement of the sensor(s), and it may be difficult to detect loss-of-contact between the sensor and the non-targeted tissue to be protected, or to sense the actual positioning of the sensor relative to the non-targeted tissue. Further, without using one or more imaging means, it is exceedingly difficult to locate a single protective thermocouple directly opposite or in the field of energy delivery of the ablating device. If such difficulty is compensated for by providing a thermocouple or thermistor array of larger area, another issue is presented, that being obtaining good thermal contact to the esophageal interior. Finally, apparent proper placement of the monitoring thermocouple using fluoroscopy still cannot guarantee proper thermal contact to the esophagus, or thermal wetted contact to the esophagus (i.e., a wet contact which stays wet and thermally sinking during an ablation procedure so as prevent the corresponding tissue from drying out and overheating).
Accordingly, there is a need for an ablation tool or system that will minimize and/or eliminate one or more of the above-identified deficiencies.